RE: Query on Number of Parses and Executions(for Selects from Views)

Hi Cary,

Thank your highlighting the same. I agree with you on calling a parse =
once and reusing the parsed cursor is the best approach. But the =
mentioned select statement in my case is a ref cursor and not a dynamic =
statement.

        I am wondering why a cursor like this should call a parse every time?. =
Additional information here is that the cursor is defined in a function =
(say function A) within a package and this function is called repeatedly =
for various values of col1,col2,col3 from another procedure (Procedure =
B) within the same package.

The pseudo code of the routine would be like

   package B is

    type cur_type is ref cursor;

    cx_curtype cur_type;

        Procedure B(some params)

            for I in <some other cursor>
            loop

               call function A(col1,col2);

           end loop;

           end procedureB;

        function A(col1, col2)

            if <some condition>  -- This condition would be true for all the =
calls in this run and hence only this cursor would be opened
                then

                       open cursor cx_curtype=20
                         for select <column_name list>,rowid
                         from <view>
                              where col1=3D:b1 and col2 =3D:b2 and =
col3=3D'N'
                               order by col5;

              else
                        open cursor cx_curtype=20
                         for select <column_name list>,rowid
                         from <view>
                              where col1=3D:b1 and col3=3D'N'
                              order by col5;
              end if;

           end function A;
          =20
     end package;

Since the same SQL statement is executed, I would expect it to reuse the =
parsed statement but in this case it doesn't. Is this a expected =
behavior with ref cursors?

Thanks again

Best Regards

Sriram Kumar
-----Original Message-----
From: oracle-l-bounce@xxxxxxxxxxxxx =
[mailto:oracle-l-bounce@xxxxxxxxxxxxx] On Behalf Of Cary Millsap
Sent: Tuesday, April 06, 2004 12:24 PM
To: oracle-l@xxxxxxxxxxxxx
Subject: RE: Query on Number of Parses and Executions(for Selects from =
Views)

Sriram,

How many parse *calls* get made is determined entirely by the
application. The application is simply telling the database to parse the
same statement 2,079 times. The Oracle kernel is smart enough to know
that only the first requires a "hard parse," but once the app tells the
db to execute a parse call, the db counts it as a parse call. ...And it
costs a lot of end-user response time to process all these parse calls:
lots of CPU and lots of network latency that shows up as time spent in
"SQL*Net message from client" timed events.

To fix the problem, pull the parse call outside of whatever loop it's in
within the application source code. If it's PL/SQL, then use the
DBMS_SQL package to extract the parse call from the loop so that you
have this:

  /* good */
  dbms_system.parse(...)
  loop
    dbms_sql.execute_and_fetch(...)
  end

...And NOT this:

  /* bad */
  loop
    execute immediate ...
  end


Cary Millsap
Hotsos Enterprises, Ltd.
http://www.hotsos.com
* Nullius in verba *

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-----Original Message-----
From: oracle-l-bounce@xxxxxxxxxxxxx
[mailto:oracle-l-bounce@xxxxxxxxxxxxx] On Behalf Of
k.sriramkumar@xxxxxxxxxxxxxxxxxx
Sent: Tuesday, April 06, 2004 1:23 AM
To: oracle-l@xxxxxxxxxxxxx
Subject: Query on Number of Parses and Executions(for Selects from
Views)

Hi Guru's
=20
    I have a query like this
=20
  select <column_name list>,rowid
  from <view>
  where col1=3D:b1 and col2 =3D:b2 and col3=3D'N'
  order by col5
=20
  1. This SQL is executed from PL/SQL and the query static in nature =20
  2. Oracle version is 9.2.0.4
  3. This query would be executed say 2000 times for various values of
col1,col2
  4. I traced the session and  tkprof output shows that number of parses
and executes are 2079.=20
=20
call     count       cpu    elapsed       disk      query    current
rows
------- ------  -------- ---------- ---------- ---------- ----------
----------
Parse     2079    216.92     233.07          0          0          0
0
Execute   2079      0.33       0.43          0          0          0
0
Fetch     5297      1.54       2.71        233      11929          0
3218
------- ------  -------- ---------- ---------- ---------- ----------
----------
total     9455    218.79     236.21        233      11929          0
3218
=20
=20
  I expected that this statement to be parsed once and executed 2079
times. why is it getting parsed 2079 times?.
=20
Also,
=20
Misses in library cache during parse: 1
=20
which means that the statement was not found in the library cache only
once...
=20
My initial guess was that the optimizer was rewriting the query but
checked query_rewrite_enabled=3Dfalse...The optimizer mode is =
RULE...would
not be able to change the optimizer_mode for now
=20
Would be great if you could throw some light on this please.
=20
Best Regards

Sriram Kumar=20


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